Memory, for example, static random access memory (SRAM) or read only memory (ROM), includes a number of memory cells. A memory cell is coupled to a word line and to one or more bit lines and can store one bit of data. The bit lines coupled to the memory cells are called primary bit lines. The primary bit lines are coupled to pass transistors and undergo various levels of multiplexing to provide multiplexed bit lines, called secondary bit lines.
Generally, the multiplexed or secondary bit lines are coupled to two sensing nodes of a sense amplifier such as a single-ended sense amplifier and a double-ended sense amplifier. The sense amplifier can be of different types: a balanced sense amplifier and an unbalanced sense amplifier. In case of an unbalanced, single-ended sense amplifier, for example, one sensing node is coupled to a multiplexed bit line, while the other node is directly coupled to a power supply. The sense amplifier determines the difference in voltages on these sensing nodes to read a value of data stored in a memory cell.
In a typical read operation, a particular primary bit line is selected by activating a coupled pass transistor, which is supplied with the power supply. The power supply may get coupled to a multiplexed bit line corresponding to the primary bit line due to the inherent coupling between the pass transistor and the multiplexed bit line. Since such a power-supply coupled bit line, i.e., the multiplexed bit line, and the power supply are coupled to the two sensing nodes of a single-ended sense amplifier, any noise or fluctuation in the power supply can get coupled to these sensing nodes. As a result, an error may get introduced in an output of the single-ended sense amplifier.
A noise or fluctuation in the power supply may occur due to a variety of reasons, for example, due to charging and discharging of components including capacitors and transistors during read and write operations of the memory. To prevent these fluctuations, various methods have been implemented including increasing noise margins of the sense amplifiers, coupling a large capacitor to a power mesh, etc. However, these methods slow down the operation of the sense amplifiers and also impose an additional area penalty, which can become more pronounced for a large number of word lines in a memory.